Field of the Invention
The present invention relates to a pneumatic tire in which a sipe is formed in a land portion of a tread surface.
Description of the Related Art
Conventionally, there has been known a pneumatic tire in which a cut called as a sipe is formed in a land portion such as a block or a rib for the purpose of enhancing a traveling performance on a wet road surface or an ice road surface. A two-dimensional sipe formed into a two-dimensional shape which is not changed in its shape along a depth direction has been known as the sipe mentioned above, and a plane sipe and a wavy sipe are put to practical use. Further, a three-dimensional sipe formed into a three-dimensional shape which is changed in its shape along a depth direction has been known, and is disclosed, for example, in Patent Documents 1 to 6.
Since the two-dimensional sipe is not suppressed from deforming along a width direction of the sipe as is different from the three-dimensional sipe, an opening portion of the sipe tends to move, and the sipe is opened widely in connection with tolling motion. Further, even in the three-dimensional sipe, in the case that the sipe is formed into a two-dimensional shape in a tread surface side, like the tires described in the Patent Documents 1 and 2, the sipe is widely opened in the same manner. As a result, a so-called stone holding that a pebble on the road surface makes an intrusion into the sipe is generated in an incrementing manner, and a strain is concentrated in a sipe bottom, so that a sipe crack may be generated.
On the other hand, in the case that a whole area of a wall surface of the sipe is formed into the three-dimensional shape such as the tires, for example, described in the Patent Documents 3 to 6, the cured tire is closely attached to a mold and a mold releasing performance tends to be deteriorated. The reason is that a lot of bent portions are included in the wall surface of the three-dimensional sipe mentioned above, and a resistance at a time when a blade for forming the sipe is pulled out of the tire is great. In a both-sides closed sipe which is closed in both ends, the problem of the mold releasing performance is significant in addition to the problems of the stone holding and the sipe crack mentioned above, and a method which can improve the problem is desired.